The present invention relates to a novel antagonistic yeast useful in controlling spoilage of agricultural produce, methods of use thereof and compositions containing same. Specifically, the present invention relates to the yeast Metschnikowia fructicola and to use thereof to inhibit growth of unwanted microorganisms on a portion of a plant, for example, foliage, flowers, fruit, roots or vegetables.
One of the most serious problems in the modern produce (fruit, vegetable and flower) industry is decay or spoilage of produce after harvest. It is estimated that postharvest losses of fruits and vegetables are 50%. This loss is attributable to fungal and bacterial infections to a great degree. In developing countries, postharvest losses are often severe due to the lack of adequate handling and refrigerated storage facilities. While developed nations have adequate refrigeration, consumers in these countries often purchase produce which has been shipped great distances and stored for prolonged periods of time. Postharvest decay of fruits and vegetables can be traced to infections that occur either between flowering and fruit maturity or during harvesting and subsequent handling and storage.
Synthetic fungicides such as imazalil and thiabendazole (TBZ) have traditionally been a primary means of controlling postharvest produce loss. However, there is increasing global pressure to reduce the use of toxic chemicals in the food industry. Consumers are concerned about chemical residues on fruit and vegetables in general and are especially uncomfortable with the idea of postharvest application of chemicals.
In addition, environmentalists are becoming increasingly vocal about chemical pesticide disposal and levels of chemical residues on fresh produce.
Concurrently, fungicide-resistant strains of pathogens have emerged to most commonly used fungicides (e.g. TBZ, Imazalil, Rovral). Finally, some of the more effective fungicides such as Captan and Benlate have been deregistered and are no longer available. Further, postharvest treatment of some types of produce is not permitted. In addition, much postharvest spoilage is the result of pathogens which colonized produce prior to harvest.
All of these factors have contributed to increased interest in the development of effective alternatives which pose no risk to human health and the environment. Use of biological approaches such as natural compounds, induced resistance and antagonistic microorganisms in plants have all been proposed as potential alternatives to synthetic fungicides for prevention or control of decay of agricultural produce.
Natural compounds are typically expensive to produce and of limited efficacy. Of the biological approaches, they hold the least promise.
Induced resistance holds considerable promise in theory but has suffered from two problems in other instances where it has been tried. Induced resistance based on genetically modified organisms (GMOs) has often had disappointing results because pathogens mutate when the GMOs are widely deployed in the field. However, the more complicated problem with GMOs has proven to be resistance to GMOs in general by consumers and environmentalists.
This leaves development of antagonistic microorganisms as the remaining “acceptable” biological approach.
In recent years, research on the use of microbial biocontrol agents for the control of postharvest diseases of fruits has gained considerable attention and has moved from the laboratory to commercial application. From these efforts, a large body of information regarding the use of microbial biocontrol agent to control postharvest diseases is now available (Droby et al., 2001). The selection of putative microbial antagonists has been based mainly on the ability of antagonists to rapidly colonize fruit surfaces and wounds, out compete the pathogen for nutrients, and survive and develop under a wide range of temperature conditions. Antagonists which can be used in the presence of agricultural chemicals, including antibiotics, have not been previously characterized.
A simple and reliable screening technique for selecting antagonists has been developed utilizing the wound site as a selective medium. Utilizing these procedures and other comparable protocols, several antagonistic bacteria, yeasts, and filamentous fungi have been isolated and shown to protect a variety of harvested commodities including citrus and pome fruit against postharvest decay (Droby et al., 1989; Janisiewicz and Roitman, 1988; Chalutz and Wilson, 1990; Roberts, 1990; Droby et al., 1991; Gullino et al., 1991; Janisiewicz, 1994; Lurie et al., 1995; Chand-Goyal and Spotts, 1996; El Ghaouth et al., 1998; Ippolito et al., 2000).
The success of some of these microbial antagonists in laboratory and large scale studies has generated interest by several agro-chemical companies in the development and promotion of postharvest biological products for control rots of fruits and vegetables. A number of microbial antagonists have been patented and evaluated for commercial use in postharvest treatment of produce. Currently, four antagonistic microorganisms, two yeasts, Candida oleophila, and Cryptococcus albidus and two strains of a bacterium, Pseudomonas syringae are commercially available under the trade names ASPIRE, YieldPlus, and BIOSAVE-110 and BIOSAVE-111 respectively.
Patents describing use of bacteria and yeasts for biological control of fungal diseases of agricultural commodities include U.S. Pat. No. 5,314,691 (Coffey et al.); U.S. Pat. No. 5,270,059 (Janisiwicz et al.); U.S. Pat. No. 5,266,316 (Elad et al.); U.S. Pat. No. 5,244,680 (Roberts); U.S. Pat. No. 5,238,690 (Elad et al.); U.S. Pat. No. 5,041,384 (Wilson and Chalutz); U.S. Pat. No. 5,711,946 (Goyal and Roberts) and PCT publications WO 92/18009 (Shanmuganathan) and WO 91/01641 (Wilson et al.). Each of these prior art teachings is narrowly defined as a composition or method containing/employing a disclosed species or strain of bacteria, fungus or yeast. None of these teachings includes a micro-organism which has proved effective against a wide range of fungal pathogens in a wide range of agricultural commodities. Further, none of these patents contain a hint or a suggestion that yeast of the genus Metschnikowia are useful in preventing post harvest loss of produce.
Metschnikowia pulcherrima is known to have some efficacy in biological control of a few deleterious micro-organisms on fruit (DeCurtis et al. (1996) Ann. Microbiol. Enzymol. 46: 45–55 and Piano et al. (1997) Postharvest Biol. Technol. 11:131–140), however it is a separate and distinct species from Metschnikowia fructicola. Further, the apparently limited spectrum of antagonist activity of Metschnikowia pulcherrima renders it ill suited for use in the produce industry. Thus far, only a limited spectrum of biocontrol activity for M. pulcherrima has been demonstrated. This renders it ill suited to commercial prevention pre- and postharvest in a wide variety of agricultural settings.
There is thus a widely recognized need for, and it would be highly advantageous to have, a novel antagonistic yeast useful in controlling spoilage of agricultural produce, methods of use thereof and compositions containing same devoid of the above limitations.